slider bars start changing colors

I’m using windows Me on an 800MHz pentium III computer with 768MB of RAM and a 40GB hard drive (about 30GB still free). After operating for an hour or so, the start button and the arrow ends of slider bars(both horizontal and vertical) start changing colors. they become a jumble of miscellaneous colors and are a bit more difficult to grab with the mouse. This happens with all application and seems to reset to normal if i turn the computer off and then on again. Then the problem resurfaces. Haveyou seen this? Any suggestion?